List/Add members for groups/corpus/repositories

A new generic component must allow a user to add other users & groups to targets under his control.

This component must allow:

• listing current users & groups on the target
• listing all the user groups
• selecting one of those group to add it (create a right)
• adding a user directly through its email address

This could of course be split in several MR (list current rights, list & add groups, add user)

We should have 2 buttons on top:

• Add a group open a modal listing all the groups that the user has access to. That modal allow selecting a group, and creating the right immediately
• Add a user open a modal with a single text input to enter the target user's email address